Testing of data processing systems is important to ensure proper operation. Testing may be performed in a factory following manufacture and prior to using the data processing system in a user application. The factory testing ensures an end user receives a properly functioning product. However, during operation of the data processing system by an end user, it may also be desirable to test the data processing system so that any failures which occur during normal operation of the product can be detected.
A well known technique to permit integrated circuits to be tested during operation is the use of logic testing registers, called Multiple Input Shift Register (MISR). Multiple input shift registers implement any of a variety of polynomials by receiving data from various internal nodes of the integrated circuit and performing signature compression and accumulation. The signature compression and accumulation is a series of logic operations which result in a single output value known as a signature value. The signature value is compared with a desired value to determine whether the integrated circuit being tested is functioning correctly.
Since the testing of the integrated circuit is performed on-line or while the integrated circuit is functioning in a real-world application, the circuitry for implementing the MISR and associated control must be implemented within the integrated circuit. Due to the size of a MISR and therefore expense, the number of MISRs and the implementation size of a MISR may be limited. As a result the ability to test the integrated circuit is severely limited.
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